Differential Expression of Human and Bacterial Proteins Re- 2 veals Microbiome–Host Crosstalk in Metabolic Disorders

The rising global prevalence of obesity and related disorders, including metabolic syn-drome (MetS) and type 2 diabetes (T2DM), highlights the need to better understand the mechanisms underlying these conditions, particularly host–microbiota interactions. While the gut microbiota has been extensively studied, the role of the oral microbiota and its interaction with human salivary proteins remains poorly explored. This study investigated the integrated human salivary proteome and bacterial metaproteome in Brazilian individuals spanning different metabolic states: normal weight, overweight, obesity, MetS, and T2DM. Saliva samples were analyzed using mass spectrome-try-based proteomics to identify differential protein profiles. The results revealed sig-nificant downregulation of the human proteins MYSM1 and GAD65 in obesity, MetS, and T2DM, with negative correlations to BMI, suggesting compromised an-ti-inflammatory functions. In contrast, carbonic anhydrase VI (CA6) was markedly upregulated and positively correlated with systolic blood pressure and glucose levels, indicating an acidic and inflammatory oral environment. In the bacterial metaprote-ome, TrxC-2, UMPK, and RsmH were significantly increased in metabolically com-promised groups and positively associated with anthropometric and insulin resistance markers, reflecting microbial adaptations to oxidative stress and enhanced virulence. Interactome analysis revealed negative correlations between bacterial proteins and MYSM1/GAD65, alongside positive associations with CA6, suggesting a feedback loop between oral dysbiosis and host metabolic dysfunction. These findings highlight the oral cavity as a key site of host–microbiota interaction in metabolic diseases and iden-tify potential biomarkers and therapeutic targets.